If all five people on a team no longer want to continue playing a match, none of them should be penalized for leaving.
It's not an uncommon situation: the enemy team has a 15k net worth advantage and their carry has two more items than yours does, but they don't make that last push to actually finish the game. As much as it might be true that every game is winnable, there comes a point when a team collectively would just like to throw in the towel and move on to the next one.
Locking the two teams in a cage match where neither of them can leave until the other allows them to isn't fun game design – it's sadistic. I have played enough games where being on the winning side of one of these stomps is not even fun, it's tedious.
I personally would come back to dota more often if something like this was implemented. What do you guys think?